In my head I thought one could make relatively cheap high capacity in 2.5" SATA form factor by having more NAND chips of lower capacity. You give up speed and PCB space but that's fine since bandwidth and IOPS are limited by SATA anyway and there's plenty of space compared to M.2.

Turns out to not shake out that way, controller ICs that support SATA aren't coming out any more, and NAND ICs are internally stacked to use up channels while not taking up PCB space.

There are some enterprise options, but they're mad expensive.